Exchange stop receiving mail and gives the error 4.1.3 Insufficient system resources. You may also see errors in the event viewer like:
The Microsoft Exchange Transport service is rejecting message submissions because the available disk space has dropped below the configured threshold.

The drive that the Queue database is on is running out of space. You can either free up some space on that drive or it can be moved to one that has more space. It's location can be found in the C:\Program Files\Microsoft\Exchange Server\Bin\EdgeTransport.exe.config file in the QueueDatabasePath variable.

In order to move the database stop the Microsoft Exchange Transport service and move the database from C:\Program Files\Microsoft\Exchange Server\TransportRoles\data\Queue to a new location. Make sure the new location has the following permissions:

Network Service: Full Control System: Full ControlAdministrators: Full Control